1. Field of the Invention
The present invention relates to needleless sample sites through which fluids are injected or withdrawn from a patient's circulatory system and, more particularly, to such a sample site through which a whole blood sample may be taken.
2. Description of the Prior Art
Sample sites typically comprise a housing through which fluids flow and which is in-line with tubing connected to a patient's circulatory system. Blood may be withdrawn through the sample site by inserting a needle or the blunt canula tip of a syringe, for example, into the housing through a seal in the sample site housing and withdrawing the fluid inside the housing.
An exemplary system which may advantageously employ a sample site for withdrawing blood is a blood pressure monitoring system in which a catheter inserted into a patient's blood vessel is connected via tubing to a blood pressure sensor, and a stopcock, which either connects the tubing to a supply of saline solution or a reservoir. A sample site may be included in-line with the tubing blood sampling without an additional needle puncture to the patient.
When the tubing is connected through the stopcock to the saline source, the sensor is in fluid communication with the patient's circulatory system to sense the patient's blood pressure. When it is desired to take a sample of the patient's blood, rather than puncturing the patient with another needle, the sample site may be used. To this end, the stopcock is turned to disconnect the saline source from the patient's circulatory system to the reservoir. Saline will flow away from the patient and into the reservoir as the patient's blood flows through the tubing and into and through the sample site. Thereafter the needle of a syringe or the syringe tip itself is inserted into the sample site and blood is withdrawn therefrom with the syringe. The needle or syringe tip is then removed from the sample site after which the stopcock is turned to disconnect the patient's circulatory system from the reservoir, reestablishing the connection between the patient's circulatory system and the saline source so as to reestablish the blood pressure monitoring function.
When using a sample site as in the above-described system, it is desirable that whole blood be removed from the patient through the sample site. That is, it is desirable that the blood removed through the sample site not be mixed with any other fluid, such as the saline solution normally present in the sample site during blood pressure monitoring. Where the sample site is for needle-based use, such as where the seal is a latex plug that only a needle may pierce (i.e., a blunt cannula is not usable), all of the saline may be displaced from inside the housing during a sampling operation by the use of flow directors in the sample site inlet and/or outlet port(s) as described in co-pending application Ser. No. 07/746,239, filed Aug. 15, 1991, the disclosure of which is incorporated by reference as if set forth fully herein. While such port-located flow directors are believed to provide undiluted whole blood samples for needle-based systems, port-located flow directors may not always be sufficient to flush the sample site in non-needle-based or needleless systems due to the operation of the seal and any related valve structure.